var zuo = 0;
		
		function yi_dong()
		{
			var oUl = document.getElementById("aaa");
			
			zuo = zuo - 2;
			if(zuo < - 900)
				zuo = 0;
			
			oUl.style.left = zuo + "px";
		}
		
		var zhong = null;
		
		function nao_zhong()
		{
			clearInterval(zhong);
			zhong = setInterval(yi_dong,30);
		}